Notice that the mother told the elderly neighbor that the father wanted to see the children but "her boyfriend said no".
An unrelated individual - not even a stepfather - has better protective instincts regarding the children than their own mother.
Execute the father - supervise the mother who either has the IQ of a turnip or is a total doormat (maybe both).
She's just as guilty. Impale them both in the public square and leave their corpses to rot on the pikes as a warning.